distant Asian sites and, therefore, to unveil the relative chronology of the earliest human migrations in Southeast Asia. This uncertainty can be explained by several factors: the stratigraphic and geographic dispersal of fossils over such a large territory, decontextualized discoveries by inhabitants, and dating discrepancies. The first discoveries of artifacts and, later, of hominid fossils in the Sangiran dome were reported by von 4 Koenigswald in the 1930s ( ). The hominid fossils found led to descriptions of two new species - Meganthropus paleojavanicus Pithecanthropus dubius Pongo and - along-side sp. and the archaic and classic Pithecanthropus Homo erectus. 1 groups of ( ) This hominid taxonomic richness is still under study ( ) and has spurred interdisciplinary work by Indonesian-German, -Japanese, -American, and -French teams. A lithostratigraphic framework (study of strata rocks facies) consolidated by biostratigraphic observations (assigning ages to rock strata using fossils) emerged in the second half of the 20th century. Hominid fossils have been attributed, with some incertitude, to the upper part of the Sangiran black-clay formation, the upper- lying boundary Grenzbank conglomeratic layers, and Bapang fluviovolcanic formation. For 25 years, two chronological frameworks for this sedimentary sequence have been facing off. One presents a 'younger' chronology for the hominid fossil layers [from between 1.3 and 1.1 million years (Ma) to between 0.7 and 0.6 Ma] and the other an 'older' chronology (from between 1.7 and 1.6 Ma to 1 Ma). The 'younger' 5 framework is based on fission-track dating (zircons, amphiboles, and tektites) ( ), K/Ar dating (amphiboles and 6 tektites), and Ar/Ar dating (amphiboles) ( ), along with paleomagnetism studies on fine-textured sediments, stratigraphic positions of Australasian tektite finds, and e lectron spin resonance dating of quartz. The 'older' 7 8 framework is based on Ar/Ar dating of pumice hornblende minerals ( , ). Unfortunately, many publications dealing with early human migrations out of Africa have brushed this dating discrepancy problem under the carpet by referring to only one (mostly the 'older') of the two conflicting chronologies. et al. The new study by Matsu'ura makes a seminal contribution to the 'younger' chronological framework. The three pairs of new datings show a tuff (volcanic ash from eruption) below the hominid-bearing layers to be only 1.34 Ma of age, and the fossil-rich layers of the Grenzbank and lowermost Bapang formations to be <0.97 Ma and 0.88 Ma of age, respectively. The datings of the tuff and volcaniclastic layers in the new study are based on a combination of U/Pb and fission-track dating on multiple zircon grains. Until now, the oldest hominid-bearing layers at Sangiran have been included among the rare human-bearing sites outside Africa that have been dated earlier than 1.5 Ma. Previously, deposits from the Perning hominin site in East Java were dated to the competitor age of 1.6 Ma. 9 However, these deposits have been rejuvenated to an uncertain age of <1.49 Ma ( ). Therefore, a 'younger' chronology for Sangiran hominids implies that humans migrated from Asia to Southeast Asia and Java ∼ H. erectus 300,000 years later than previous estimates. This means that 's arrival on Javanese sites took place a step later relative to the Dmanisi (Georgia) and Lantian or Nihewan basin sites (China) (see the figure). H. erectus In the Sangiran dome area, the oldest fully terrestrial layers constrain the first potential apparition of fossils. These layers were characterized by in situ pedogenetic traces and terrestrial taxon stratigraphic positions. Such traces are found in the upper part of the Sangiran black-clay formation, with the underlying tuff et al. dated, by Matsu'ura , to 1.3 Ma. This date can be taken as a maximal age for local hominid discoveries; however, other sites in the wider regional sedimentary basin could bear older, fully terrestrial deposits, which should be studied. In the middle of hominid-bearing strata, the Grenzbank layers, are fossil- and artifact-rich beds, now anchored at 0.9 Ma (1.6 to 1.5 Ma in the 'older' chronology). Drastic worldwide changes, such as the sea level drop of 120 minduced by the first 100,000-year global glaciation cycles, began about 0.9 to 0.86 Ma. During this H. erectus period, immigration via the Asian Sunda Shelf (see the figure) of new fauna and classic populations must have strongly affected the preestablished hominid species. Researchers have yet to discover who lived with (or replaced) whom in Sangiran. For example, the hominid- rich layers of the Grenzbank zone include fossils from at least three hominid species, who might or might not have lived in the same ecosystem, depending on diachronism of this boundary layer at the dome's scale. A challenge regarding local Sangiran hominids is to correlate sedimentary sequences of remote hominid findspots through tephrostratigraphy, which uses the geochemical characteristics of tuffs (such as volcanic glass) to